"However, feeding or administering NAD+ directly to organisms is not a practical option. The NAD+ molecule cannot readily cross cell membranes to enter cells, and therefore would be unavailable to positively affect metabolism. Instead, precursor molecules to NAD+ must be used to increase bioavailable levels of NAD+."

Does this go contrary to what we currently understand which is NR or NMN is consumed orally, liver converts to NAD+ which is then distributed via the bloodstream to the cells of the body?

No, because that isn't what we currently understand, which is rather that after NR or NMN is consumed orally, it is converted to NAD+ in the liver, following which various NAD+-consuming enzymes convert it to NAM, which is then distributed via the bloodstream to the cells of the body. As it says, it's generally though not universally agreed that NAD+ doesn't cross cell membranes in either direction.

No, because that isn't what we currently understand, which is rather that after NR or NMN is consumed orally, it is converted to NAD+ in the liver, following which various NAD+-consuming enzymes convert it to NAM, which is then distributed via the bloodstream to the cells of the body. As it says, it's generally though not universally agreed that NAD+ doesn't cross cell membranes in either direction.

So really, are we back to the possibility that just taking NAM on exercise days (NAMPT) is useful for age 40+ adults is the best option money wise? I read your posts on NR performing better but now I'm just wondering if this is even useful at all. There are new ways coming out that look at increasing NAD+ through another pathway.

I wish part of this study would look at not just NMN but NR and NAM as well as CD38 inhibition, heat stress and senescent cell removal (eliminating SASP as a factor in NAD+ decline) in just wild type mice. So several side by side experiments with a control.